1. Field of the Invention
The invention relates to the apparatus which is useful for the rapid, accurate, self-correcting and theoretically correct measurements of the state of birefringence in selected planes within a birefringent body, and, in particular, to determine photoelastic isodynes in selected planes which carry information on the normal and shear stress components in the whole field.
The measurements are simple when the stress state is two-dimensional (plane).
While the apparatus has application for whole field measurements of a wide range of birefringence states in solid and liquid bodies, the following description is taken by way of example with respect to a measurement system for the determination of stress components in engineering objects, in particular, to the measurement system for the determination of components of plane stress states.
2. The Prior Art
The whole field measurements of plane stress fields usually utilize some characteristic lines of two-dimensional stress fields such as isochromatics (lines of constant values of maximal shear stresses), isoclinics (lines of constant directions of principal stresses), isopachics (lines of constant values of the sum of principal stresses), etc. For instance, transmission polariscope techniques supply fields of isochromatics and isoclinics; that is, they supply two independent pieces of information when three independent data on stress components are needed to determine a plane stress state. To determine all three stress components at all points of a plane stress state using the transmission photoelasticity techniques it is necessary to apply additional relations which decrease the reliability and accuracy of calculated values of stresses.
The sometimes used scattered light technique based on photographic recording of light scattered from the points within a body illuminated by a stationary sheet of light is theoretically and practically inaccurate: the observation and azimuthal angles of the scattered light change from point to point, and the angle between the object plane and the image plane is close to 45.degree. instead of being close to zero.